The invention relates to a process for stepwise heating metallic strips or foils of more that 800 mm in width to an end temperature of 100.degree. to 300.degree. C. Furthermore, the invention relates to the use of this process in the manufacture of composites and in the laminating and lacquering or painting of metallic strips or foil.
Known from the Canadian Pat. No. 857 845 is a process for manufacturing flat building panels made up of a relatively thick core of thermoplastic plastic and relatively thin outer layers of metal. In that process aluminum sheets, for example 0.3 mm thick, are pressed by a pair of rolls heated to 70.degree. C. onto a core layer which is still hot and bears a molten adhesive film on the surface. Before making contact with the core layer, the cold metal strips are heated to 70.degree. C., at maximum, by the pre-heated rolls. Experience shows that such laminates have a relatively strong tendency to form wrinkles when subsequently worked, especially after cooling.
A known method to avoid such wrinkles in composite panels is to heat the metal strips before laminating, using infra-red radiation, gas flame or hot air for that purpose.
Thus, according to the Swiss Pat. No. 478 652 use is made of a continuous throughput furnace with three successive heating zones for heating up, holding the metal strip at temperature and cooling down. It turns out that regulating the temperature profile accurately over the width of the strip is extremely difficult.
The Swiss Pat. No. 478 652 exhibits therefore the following disadvantages, as do the other known heat sources for heating up strip or foil:
poor thermal efficiency PA0 danger of overheating if the continuous process is suddenly stopped e.g. in emergency PA0 for high production rates one requires voluminous machine elements which are expensive to purchase and maintain PA0 with wide sheets the temperature distribution over the width is inexact, varying by 2.degree. to 5.degree. C.
The object of the present invention is therefore to develop a process for stepwise heating-up metallic strips or foils of width more than 800 mm to an end temperature of 100.degree. to 300.degree. C. such that a uniform temperature in the range of .ltoreq..+-.1.degree. C. is assured over the whole width of the strips, and that a low investmentoutlay for the device and modest running costs are possible. The process should be widely applicable.